Influence of Endogenous Parathyroid Hormone on Citrate and Lactate Production by Bone in vitro.

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Abstract
Summary Femora removed from rats with varying levels of endogenous parathyroid secretion were incubated in pooled rat serum. Samples of the media were analyzed for citrate, lactate, and C14-incorporation into these 2 acids from labelled glucose added to the incubation media. Both citrate and lactate production by bone cells decreased within 4 hours after parathyroidectomy. Differences in citrate production were readily detectable in a 2-hour incubation; 6 hours of incubation were required to show differences in lactate formation. While lactate accumulated in the media throughout the incubation, citrate reached a peak and leveled off suggesting recycling. The largest incorporation of radioactivity from glucose into citrate was also seen at 2 hours. At this time incorporation into lactate was negligible; however, by 6 hours radioactivity in lactate equalled the highest value observed for citrate. Incubation of diaphyseal and metaphyseal separately demonstrated greater citrate production in the diaphysis; conversely, the metaphysis was the site of greater lactate production. Data from the studies with radioactive glucose confirm all of the findings for total organic acid production. These data are interpreted as suggesting that there are 2 populations of bone cells which differ as to their primary end product of glucose metabolism. If parathyroid hormone has only one site of action on both these cell populations, it would seem to affect the rate of a reaction prior to the formation of pyruvate in the glycolytic pathways. Femora removed from rats with varying levels of endogenous parathyroid secretion were incubated in pooled rat serum. Samples of the media were analyzed for citrate, lactate, and C14-incorporation into these 2 acids from labelled glucose added to the incubation media. Both citrate and lactate production by bone cells decreased within 4 hours after parathyroidectomy. Differences in citrate production were readily detectable in a 2-hour incubation; 6 hours of incubation were required to show differences in lactate formation. While lactate accumulated in the media throughout the incubation, citrate reached a peak and leveled off suggesting recycling. The largest incorporation of radioactivity from glucose into citrate was also seen at 2 hours. At this time incorporation into lactate was negligible; however, by 6 hours radioactivity in lactate equalled the highest value observed for citrate. Incubation of diaphyseal and metaphyseal separately demonstrated greater citrate production in the diaphysis; conversely, the metaphysis was the site of greater lactate production. Data from the studies with radioactive glucose confirm all of the findings for total organic acid production. These data are interpreted as suggesting that there are 2 populations of bone cells which differ as to their primary end product of glucose metabolism. If parathyroid hormone has only one site of action on both these cell populations, it would seem to affect the rate of a reaction prior to the formation of pyruvate in the glycolytic pathways.

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